1. Field of the Invention
The present invention generally relates to a method and apparatus for transmitting/receiving data in a mobile communication system, and in particular, to a method for efficiently multiplexing diversity transmission and localized transmission in an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a transmission/reception apparatus thereof.
2. Description of the Related Art
Generally, wireless communication systems have been configured for a stationary wired network which cannot be connected to terminals. A typical wireless communication system can include, for example, Wireless Local Area Network (WLAN), Wireless Broadband (Wibro), Mobile Ad Hoc, etc., all of which are referred to herein as a mobile communication system.
A mobile communication system, unlike a general wireless communication system, is premised on mobility of a user. A mobile communication system is ultimately aimed at allowing a user to exchange information media with anyone at anytime in anyplace using a mobile terminal, such as a portable phone, Personal Digital Assistant (PDA), a radio pager, etc. In addition, with rapid development of communication technology, mobile communication systems have reached a phase of providing not only general voice call service but also high-speed data service capable of transmitting high-volume digital data, such as moving images as well as email (electronic mail), still images, etc., by means of a mobile terminal.
For example, an Orthogonal Frequency Division Multiplexing (OFDM) system is a typical example of a mobile communication system that provides high-speed data service using a multi-carrier transmission scheme. An OFDM transmission scheme, a scheme for converting a serial input symbol stream into parallel signals and modulating each of them with multiple orthogonal subcarriers before transmission, has attracted public attention with the development of Very Large Scale Integration (VLSI) technology since the early 1990s.
An OFDM transmission scheme typically modulates data using multiple subcarriers. As subcarriers maintain their mutual orthogonality, an OFDM transmission scheme, compared to an existing single-carrier transmission scheme (or single-carrier modulation scheme), has a characteristic that the OFDM transmission scheme is robust against a frequency selective multipath fading channel. Therefore, an OFDM transmission scheme is a transmission scheme suitable for a high-speed packet data service, such as a broadcasting service or the like. Orthogonal Frequency Multiple Access (OFDMA), a modification of OFDM, is a technology for realizing multiple access by providing some of the available subcarriers to each user.
In a common OFDMA system, a resource allocation scheme for data transmission can be classified into diversity transmission and localized transmission according to the physical pattern of the allocated resources.
Diversity transmission, as used herein, refers to a way of transmitting data over physically distributed (or physically separated) resources, and localized transmission, as used herein, refers to a way of transmitting data over physically localized (or physically adjacent) resources.
FIG. 1 illustrates diversity transmission, localized transmission, and combined transmission of the two other transmission methods in a conventional OFDMA system.
Referring to FIG. 1, the horizontal axis indicates the frequency domain, and the vertical axis indicates the time domain. The smallest square indicates one subcarrier in the frequency domain, and indicates one OFDM symbol in the time domain. Reference numeral 101 indicates one tile, and in reference numeral 101 of FIG. 1, the tile is composed of 16 adjacent subcarriers in the frequency domain and 8 adjacent OFDM symbols in the time domain.
Commonly, one OFDM symbol is composed of multiple subcarriers, and when the OFDM symbol has the tile structure, multiple tiles are formed in the frequency domain. In the system of FIG. 1, one OFDM symbol is composed of 512 subcarriers, so there are 32 tiles in the frequency domain (512=16×32).
Reference numeral 102 indicates indexes for the tiles stated above. That is, there are tile #1 to tile #32. In FIG. 1, a part shown by the same hatching indicates data symbols being transmitted to one user. For example, a tile #1 is fully indicated by hatching of reference numeral 110, and this means that resources corresponding to the tile #1, i.e. resources of ‘8 OFDM symbols’×‘16 subcarriers’ corresponding to the tile #1, carry the data symbols being transmitted to one user. The way of transmitting data over the adjacent resources is herein called localized transmission. In the foregoing case where one tile transmits data for one user, the tile will be referred to herein as a localized transmission-dedicated tile 103, a localized tx tile, or a localized tile, for convenience.
In FIG. 1, data is transmitted to one user over the tile #1 105, data is transmitted to another user over the tile #3 106, and data is transmitted to further another user over the tile #30 108 and the tile #31 109. In this manner, multiple tiles can be used for transmitting one user data, and the multiple tiles can be either physically adjacent tiles, like the tile #30 108 and the tile #31 109, shown in FIG. 1, or physically separated tiles. When one tile is entirely used for transmitting data to one user in this way, this tile is referred to herein as a localized tile. The localized transmission scheme is a transmission scheme favored when a transmitter selects a frequency having a better channel response in the frequency domain and transmits data using the selected frequency, e.g., when a moving velocity of a user is low and the transmitter performs scheduling depending on Channel Quality Information (CQI) received from the user.
It can be appreciated in FIG. 1 that data symbols for three users are distributed in the tile #2 120, the tile #4 122 and the tile #32 124. For example, as to data transmission for the user corresponding to the part shown by hatching of reference numeral 112, data symbols for the user are uniformly distributed in the tile #2 120, the tile #4 122, and the tile #32 124. This transmission is referred to herein as diversity transmission, and the diversity transmission scheme is a transmission scheme commonly favored when a transmitter has difficulty in selecting a good channel environment in the frequency domain for transmission, i.e., favored for the case where due to the very high moving velocity of the user, even though the transmitter receives channel quality information from the mobile terminal, reliability of the channel quality information is too low at the actual data transmission time because the channel has already been changed, so the transmitter cannot depend on the received channel quality information.
The diversity transmission transmits data symbols over multiple tiles, and in this case, the multiple tiles are referred to herein as diversity transmission-dedicated tiles 104, diversity Tx tiles, or diversity tiles, for convenience.
Therefore, in FIG. 1, the tile #2 120, the tile #4 122 and the tile #32 124 are diversity transmission-dedicated tiles.
As described above, an OFDMA communication system should simultaneously support users having a high moving velocity and users having a low moving velocity. To this end, a need exists for a method of efficiently configuring and managing the diversity transmission-dedicated tiles 104 and the localized transmission-dedicated tiles 103.